V4L2: VIDIOC_QUERYBUF returns invalid argument

Hi,

In an attempt to see how V4L2 programming works, I try to write a little capture
program. The program below returns an invalid argument in the VIDIOC_QUERYBUF
ioctl:

[gert@viper v4l2]$ gcc -O2 v4l2_cap.c
[gert@viper v4l2]$ ./a.out 
image size: 152064
2 buffers granted
VIDIOC_QUERYBUF: Invalid argument
[gert@viper v4l2]$ 

What am I overlooking?

-- Gert


driver  : bttv-0.8.31
kernel  : 2.4.15
patches : 10_videodev-2.4.15-pre6.diff
          11_v4l2-2.4.15-pre6.diff
          12_userdma-2.4.15-pre6.diff


v4l2_cap.c:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev.h>

#define HSIZE 352
#define VSIZE 288
#define NUM_BUFFERS 2

struct buffer {
	struct v4l2_buffer vidbuf;
	char* data;
	int length;
};

int main()
{
	struct v4l2_capability vidcap;
	struct v4l2_format fmt;
	struct v4l2_requestbuffers reqbufs;
	struct buffer cap_bufs[NUM_BUFFERS];

	int fd;
	int i;
	
	if((fd = open("/dev/video", O_RDWR)) < 0) {
		perror("open");
		exit(-1);
	}

	if(ioctl(fd,  VIDIOC_QUERYCAP, &vidcap) < 0) {
		perror("VIDIOC_QUERYCAP");
		exit(-1);
	}

	if (vidcap.type != V4L2_TYPE_CAPTURE) {
		fprintf(stderr, "Error, not a capture device\n");
		exit(-1);
	}
	if(!(vidcap.flags & V4L2_FLAG_STREAMING)) {
		fprintf(stderr, "Error, streaming capture not supported\n");
		exit(-1);
	}

	memset(&fmt, 0x0, sizeof(fmt));
	fmt.type =  V4L2_BUF_TYPE_CAPTURE;
	fmt.fmt.pix.pixelformat =  V4L2_PIX_FMT_YUV420;
	fmt.fmt.pix.flags = V4L2_FMT_FLAG_INTERLACED;
	fmt.fmt.pix.width = HSIZE;
	fmt.fmt.pix.height = VSIZE;
	if(ioctl(fd, VIDIOC_S_FMT, &fmt) < 0) {
		perror("VIDIOC_S_FMT");
		exit(-1);
	}
	printf("image size: %d\n", fmt.fmt.pix.sizeimage); 
		
	reqbufs.count = NUM_BUFFERS;
	reqbufs.type = V4L2_BUF_TYPE_CAPTURE;
	if(ioctl(fd, VIDIOC_REQBUFS, &reqbufs) < 0) {
		perror("VIDIOC_REQBUFS");
		exit(-1);
	}
	printf("%d buffers granted\n", reqbufs.count);
	
	for(i=0; i<reqbufs.count; i++) {
		struct v4l2_buffer *vidbuf = &cap_bufs[i].vidbuf;
		
		vidbuf->index = i;
		vidbuf->type = V4L2_BUF_TYPE_CAPTURE;
		if(ioctl(fd, VIDIOC_QUERYBUF, vidbuf) < 0) {
			perror("VIDIOC_QUERYBUF");
			exit(-1);
		}



	
	}	

	close(fd);
	return 0;
}